12,961 research outputs found
Ionizing radiation fluctuations and large-scale structure in the Lyman-alpha forest
We investigate the large-scale inhomogeneities of the hydrogen ionizing
radiation field in the Universe at redshift z=3. Using a raytracing algorithm,
we simulate a model in which quasars are the dominant sources of radiation. We
make use of large scale N-body simulations of a LambdaCDM universe, and include
such effects as finite quasar lifetimes and output on the lightcone, which
affects the shape of quasar light echoes. We create Lya forest spectra that
would be generated in the presence of such a fluctuating radiation field,
finding that the power spectrum of the Lya forest can be suppressed by as much
as 15 % for modes with k=0.05-1 Mpc/h. This relatively small effect may have
consequences for high precision measurements of the Lya power spectrum on
larger scales than have yet been published. We also investigate another
radiation field probe, the cross-correlation of quasar positions and the Lya
forest. For both quasar lifetimes which we simulate (10^7 yr and 10^8 yr), we
expect to see a strong decrease in the Lya absorption close to other quasars
(the ``foreground'' proximity effect). We then use data from the Sloan Digital
Sky Survey First Data Release to make an observational determination of this
statistic. We find no sign of our predicted lack of absorption, but instead
increased absorption close to quasars. If the bursts of radiation from quasars
last on average < 10^6 yr, then we would not expect to be able to see the
foreground effect. However, the strength of the absorption itself seems to be
indicative of rare objects, and hence much longer total times of emission per
quasar. Variability of quasars in bursts with timescales > 10^4yr and < 10^6 yr
could reconcile these two facts.Comment: Submitted to ApJ, 21 pages, 17 postscript figures, emulateapj.st
Spin- and isospin-polarized states of nuclear matter in the Dirac-Brueckner-Hartree-Fock model
Spin-polarized isospin asymmetric nuclear matter is studied within the
Dirac-Brueckner-Hartree-Fock approach. After a brief review of the formalism,
we present and discuss the self-consistent single-particle potentials at
various levels of spin and isospin asymmetry. We then move to predictions of
the energy per particle, also under different conditions of isospin and spin
polarization. Comparison with the energy per particle in isospin symmetric or
asymmetric unpolarized nuclear matter shows no evidence for a phase transition
to a spin ordered state, neither ferromagnetic nor antiferromagnetic.Comment: 8 pages, 6 figure
Microscopic three-body force for asymmetric nuclear matter
Brueckner calculations including a microscopic three-body force have been
extended to isospin asymmetric nuclear matter. The effects of the three-body
force on the equation of state and on the single-particle properties of nuclear
matter are discussed with a view to possible applications in nuclear physics
and astrophysics. It is shown that, even in the presence of the three-body
force, the empirical parabolic law of the energy per nucleon vs isospin
asymmetry is fulfilled in the whole asymmetry range
up to high densities. The three-body force provides a strong
enhancement of symmetry energy increasing with the density in good agreement
with relativistic approaches. The Lane's assumption that proton and neutron
mean fields linearly vary vs the isospin parameter is violated at high density
in the presence of the three-body force. Instead the momentum dependence of the
mean fields is rather insensitive to three body force which brings about a
linear isospin deviation of the neutron and proton effective masses. The
isospin effects on multifragmentation events and collective flows in heavy-ion
collisions are briefly discussed along with the conditions for direct URCA
processes to occur in the neutron-star cooling.Comment: 11 pages, 7 figure
International Legal Review of the Relationship between International Tax Law and National Tax Sovereignty: Theoretical Foundation and Development Practices
By examining their theoretical basis and exercising practice relationship between national sovereignty and international tax law, it is demonstrated that the international tax law results from the coordination to exercise national sovereignty in the international law. Given the modern connotation of national sovereignty and exercising practices of international tax treaties in the international law, it is reasoned that âthe international tax treaty is a kind of limitation or mitigation to national tax sovereigntyâ is a false pseudo-proposition; International tax regime has been established on the international law level and constitutes a part of customary international law, which is of great significance; No country has the law-making capacity or its national interest dives in the international law to change the existing international tax regime. Taking account of the exercise of the national tax sovereignty under the backdrop of the latest development practices in international tax law, it can be found that international tax cooperation makes the exercise of national tax sovereignty increase other than decrease; Countriesâ intensive actions to safeguard their own international taxation interests strengthen the exercise of their national tax sovereignty; New international tax topics, such as Carbon tariff and environmental taxes, will accelerate law-making revolution of international law in the field of international tax law, and thus makes the exercise of national tax sovereignty to be unified.preprin
Institutional Fragmentation and the Ontological 'Ethos' of International Law as a Legal System in a World Society
In the âinstitutional fragmentation of international IP lawâ debate, the analogy between international law and national legal systems, as the theoretical premise of the âinstitutional fragmentationâ language, fails for the lack of ârelevant similarityâ. And secondly, the ontological âethosâ of international law, which are the inherent virtues of international law-making and implementation, regime evolution and interaction in this world society, could rectify the chaos of this rhetoric of âinstitutional fragmentationâ and illuminate the understated benefits as well as rationalities of institutional fragmentation. The âpost-ontological eraâ is not coming yet for this âinstitutional fragmentationâ debate, and the âinstitutional fragmentationâ is the ânew normalâ. Thirdly, The fundamental contradiction contained in this âinstitutional fragmentation of international lawâ debate is between the specialization of international law (the âfunctional approachâ of modern international lawâs development, as the endogenous factors) and top-down systematic theoretical conception of international law (international law as a legal system, as the exogenous factors). The junction of those forces is the âconcerns on the legitimacy of international lawâ against national legal systems in a world society. Fourthly, from analogical reasoning to ontological âethosâ, there is a âparadigm shiftâ from the traditional âtop-downâ global governance paradigm (which is associated with analogical reasoning and hierarchical solutions to âregime complexâ) to a âbottom-upâ approach with more ontological and inside-out-looking (which could better grasp and understand the dynamics and pulse of regime interaction and evolution). This fundamental change enables those arguments thereafter on the regime interactions and evolutions have totally different theoretical departures, journeys and destinations. Namely, it is more appropriate to ask âwhat is the status quo, and how to understand it in a historical, relational, structural and holographic way; through analyses of underlying reasons and rules, how will the landscape develop in the future and what could or should be done if there are certain preferencesâ with a realistic âbottom-up approachâ in consideration of the âlaw of universal gravitationâ and the structure of âtensional integrityâ in this âregime interactionâ perspective, rather than constructively and blindly ask âhow to better manage the existing regimes and their collisions, and what are those workable (hierarchical or top-down-governance) solutionsâ from the perspective of âtop-downâ governance with cognitive path-dependence.preprin
Extended quark mean-field model for neutron stars
We extend the quark mean-field (QMF) model to strangeness freedom to study
the properties of hyperons () in infinite baryon matter and
neutron star properties. The baryon-scalar meson couplings in the QMF model are
determined self-consistently from the quark level, where the quark confinement
is taken into account in terms of a scalar-vector harmonic oscillator
potential. The strength of such confinement potential for quarks is
constrained by the properties of finite nuclei, while the one for quark is
limited by the properties of nuclei with a hyperon. These two
strengths are not same, which represents the SU(3) symmetry breaking
effectively in the QMF model. Also, we use an enhanced coupling with
the vector meson, and both and hyperon potentials can be
properly described in the model. The effects of the SU(3) symmetry breaking on
the neutron star structures are then studied. We find that the SU(3) breaking
shifts earlier the hyperon onset density and makes hyperons more abundant in
the star, in comparisons with the results of the SU(3) symmetry case. However,
it does not affect much the star's maximum mass. The maximum masses are found
to be with hyperons and without hyperons. The
present neutron star model is shown to have limitations on explaining the
recently measured heavy pulsar.Comment: 7 pages, 7 figures, Phys. Rev. C (2014) accepte
- âŠ